Method of producing semi-conductive electrode systems



Nov. 12, 1963 P. J. w. JOCHEMS 3,110,637

METHOD OF PRODUCING SEMICONDUCTIVE ELECTRODE SYSTEMS Filed Jan. 7, 1959 INV ENTOR PIETER JOHANNES WILHELMUS JOO-IEMS United States Patent NETHOD 0F PRODUCING SEMI-(IQNDUCTIVE ELECTRODE SYSTEMS Pieter Johannes Wiihelmus .lochems, Emmasingel, Eindhoven, Netherlands, assignor to North American Philips (Iompany, Inc., New York, N.Y., a corporation of Delaware Filed Jan. 7, 1959, Ser. No. 785,374

Claims priority, application Netherlands .lan. 14, 1958 2 Claims. (Cl. 148-485) This invention relates to a method of producing semiconductive electrode-systems, such as transistors and crystal diodes, which contain a semi-conductive body, which may, for example, consist of germanium or silicon, to which at least one electrode is alloyed which consists of an alloy of aluminum and at least one other component.

It has already been suggested to produce such systems by making small bodies, for example pellets, of an alloy containing aluminum and alloying them to the semiconductor bodies.

It has been found that such alloys, even if they contain a very slight amount of aluminum, do not adhere satisfactorily to the semi-conductor bodies, presumably owing to the property of these alloys to be coated spontaneously with a thin film of aluminum oxide when in contact with oxygen.

It is an object of the present invention to provide a method in which electrodes containing aluminum can be produced in a simple manner. The invention is based on the recognition of the fact that aluminum or an alloy containing aluminum can be more readily caused to fuse with a metal or an alloy which has already been alloyed to a semi-conductor body than with the semi-conductor bodies themselves.

According to the invention, another component of the electrode finally to be produced is alloyed to the semiconductor body after which aluminum is placed on this alloyed component and finally is fused therewith. The aluminum can be applied either as a pure metal or in the form of an alloy with another element. The amount of aluminum or aluminum-alloy added in this manner can be small so that the proportion of aluminum of the finally produced electrode is less than 5%.

Preferably the aluminum or the alloy containing alu minum is added to the alloyed component as a fine powder dispersed in a binder. This component preferably is in the solid state when the aluminum is applied.

This simple application is made possible by the fact that the amount of applied aluminum may vary between comparatively wide limits.

In order that the invention may be readily carried out, two embodiments whereof will now be described by way of example with reference to the accompanying diagrammatic drawings, which are cross-sectional views of a transistor in successive stages of its production.

On a semi-conductor body 1 consisting of n-type germanium having a specific resistivity of 3 ohm-cm. and a thickness of 150 microns there is placed a pellet 2 of lead (FIG. 1). The two members are fused to one another in a jig (not shown) at 600 C. so that an alloyed body 3 is formed (FIG. 2). This body consists of lead which has absorbed a small amount of germanium.

After the assembly has been reversed, this process is repeated on the other side (FIG. 3).

Now a small amount of a dispersion 4 of 40 gms. of powdered aluminum in a solution of 20 gms. of methacrylate in cos. of Xylene is applied to both bodies (FIG. 4). The applied amount of the dispersion is not critical.

After the dispersion agent has evaporated, the assembly is again heated to 750 C. so that fusion recurrs. After cooling it is found that the electrodes 5 produced (FIG. 5) have absorbed an amount of aluminum such that they form rectifying contacts having a high emitter efiiciency.

Furthermore a base contact 6 consisting of a nickel wire can be applied to the body 1 in the usual manner with the aid of tin solder '7.

Alternatively a similar method can be used in which there is substituted for the powdered aluminum in the dispersion a powder consisting of 28% of aluminum and 72% of silver. This melts at about 560 C., and can be fused with the already alloyed component 3 at a temperature slightly higher than this melting point, for example 600 C.

' What is claimed is:

1. A method of forming a p-type region in a body of semiconductor material, comprising fusing and alloying to said body a mass of metal, cooling the fused mass to form a solid alloyed electrode on the body, thereafter painting said solid alloyed electrode with finely-divided aluminum dispersed in a liquid binder to form a layer thereon, thereafter drying the layer, refusing the mass and layer to incorporate the aluminum into the electrode and into an underlying portion of the body, and thereafter cooling the mass to solidify same in contact with the body.

2. A method of forming a rectifying contact to an n-type body portion of germanium semiconductor material, comprising fusing and alloying to said body portion a mass of lead, cooling the fused mass to form a solid alloyed electrode on the body, thereafter painting said solid alloyed electrode with finely divided aluminum dispersed in a liquid binder to form a layer thereon, wherein the dispersion contains an amount of aluminum at which the final electrode contains more than zero but less than 5% of aluminum, thereafter drying the layer, refusing the mass and layer to incorporate the aluminum into the electrode and into an adjacent region of the body, and thereafter cooling the mass to solidify same in contact with the body forming a rectifying contact thereto having a high emitter efficiency.

References Cited in the file of this patent UNITED STATES PATENTS 2,701,326 Pfann et al. Feb. 1, 1955 2,781,481 Armstrong Feb. 12, 1957 2,816,850 Haring Dec. 17, 1957 2,833,678 Armstrong et a1. May 6, 1958 2,862,840 Kordalewski Dec. 2, 1958 2,931,743 Rittmann Apr. 5, 1960 2,932,594v Mueller Apr. 12, 1960 2,937,961 Wolsky May 24, 1960 

2. A METHOD OF FORMING A RECTIFYING CONTACT TO AN N-TYPE BODY PORTION OF GERMANIUM SEMICONDUCTOR MATERIAL, COMPRISING FUSING AND ALLOYING TO SAID BODY PORTION A MASS OF LEAD, COOLING THE FUSED MASS TO FORM A SOLID ALLOYED ELECTRODE ON THE BODY, THEREAFTER PAINTING SAID SOLID ALLOYED ELECTRODE WITH FINELY DIVIDED ALUMINUM DISPERSED IN A LIQUID BINDER TO FORM A LAYER THEREON, WHEREIN THE DISPERSION CONTAINS AN AMOUNT OF ALUMINUM AT WHICH THE FINAL ELECTRODE CONTAINS MORE THAN ZERO BUT LESS THAN 5% OF ALUMINUM, THEREAFTER DRYING THE LAYER, REFUSING THE MASS AND LAYER TO INCORPORATE THE ALUMINUM INTO THE ELECTRODE AND INTO AN ADJACENT REGION OF THE BODY, AND THEREAFTER COOLING THE MASS TO SOLIDIFY SAME IN CONTACT WITH THE BODY FORMING A RECTIFYING CONTACT THERETO HAVING A HIGH EMITTER EFFICIENCY. 